1. Field of the Invention
The present invention relates in general to a parallel coupled line filter and a fabrication method thereof, and more specifically, to a miniaturized parallel coupled line filter and a fabrication method thereof.
2. Description of the Related Art
In recent years, demands on information technology and radio communication have been rapidly growing. To meet such demands, high performance radio communication equipment has been developed. Currently, however, developing miniaturized radio communication equipment which may be conveniently carried has become a major issue. As part of the ongoing development of miniaturized radio communication equipment, a lot of attention has been drawn to a filter, which is a key component of the radio communication equipment.
Since micro strip filters and Co-Planar Waveguides (CPWs) using planar transmission lines have simple structures and are easy to fabricate, they have been preferably used in radio communication equipment. Naturally, many efforts were made towards the miniaturization of these filters. Some examples of miniaturized filters are as follows.
FIG. 1 shows a miniaturized ladder filter using a slow-wave structure. Because the ladder filter in FIG. 1 has a very complicated structure, it requires a full-wave electro-magnetic (EM) simulation and has structural limitations in miniaturized design.
FIG. 2 shows another example of a miniaturized combine filter using a lumped element. The combine filter in FIG. 2 is miniaturized using a self capacitor and a mutual capacitor. Unfortunately however, extremely complicated calculation in the self capacitor and the mutual capacitor makes it more difficult to design the filter. Further, lack of accurate analysis of the combine structure adds to the difficulty of designing the filter.
FIG. 3 illustrates a hairpin filter. The hairpin filter is miniaturized by bending transmission lines. However, transmission lines can be bent only to a certain extent, so there are limitations in the fabrication of miniaturized hairpin filters.
Therefore, there is a need to develop a filter that can be miniaturized without any limitations and designed on the basis of relatively simple theoretical knowledge.
Aside from the structural limitations as aforementioned, related art filters exhibit very poor harmonic characteristics and skirt characteristics on the high frequency side are not very sharp. Accordingly, it is required to develop a scheme for miniaturizing filters and improving harmonic characteristics and skirt characteristics of the filters at the same time.